The reaction equation for ammonia synthesis is as follows:3H2+N2→2NH3+Q
Synthesis of ammonia reaction is a reversible reaction that is carried out in a reactor with a catalyst. The catalyst activity occurs within a temperature range, generally 340° C.˜520° C., at a temperature lower than 340° C. the reaction rate slows and at a temperature higher than 520° C., the catalyst loses activity to some degree due to crystal growing within The ammonia reaction is an exothermic reaction, therefore, heat exchanger is needed within in the reactor to remove excess thermal energy, to maintain the temperature of the reacted gas lower than ≦520° C., while keeping the un-reacted gas heated to ≧340° C.
The reaction rate is related to the reaction driving force, which is the difference between the reaction temperature and the equilibrium temperature within the catalyst activation temperature range. The greater the difference, the greater the reaction driving force, and the greater the reaction rate. Since the equilibrium temperature lowers as the reaction progresses, the reaction temperature in the later stages of the catalyst lifetime is lowered.
FIG. 1 is a prior art ammonia synthesis system and process. The system has an indirect heat exchange ammonia reactor 200, in which the ammonia reactor 200 is a separate unit from the waste heat boiler 202. The ammonia synthesis system comprises an ammonia reactor 200, a steam super-heater 201, a waste heat boiler 202, a supply water heater 203, a recycle gas heat exchanger 201, a water cooler 205, a refrigeration exchanger 206, a first ammonia chiller 207, a second ammonia chiller 208, a horizontal ammonia separator 209, a liquid ammonia tank 210 and a recycle compressor 211.
The prior art process in this ammonia synthesis system has an un-reacted gas stream that exits from a recycle gas heat exchanger and that splits to three streams, which enter the ammonia reactor. The reacted hot gas stream exits the ammonia reactor from a bottom side and enters a tube-side of the steam super-heater 201, which enters the waste heater boiler 202 where heat is utilized to produce saturated steam. The saturated steam from the waste heat boiler superheated in a shell side of the steam super-heater 201. The gas stream exits from the waste heat boiler and enters the supply water heater 203, recycle gas heat exchanger 204, water cooler 205, refrigeration exchanger 206, first ammonia chiller 207 and second ammonia chiller 208 where it is cooled down stepwise through the process. The gas stream enters a horizontal ammonia separator 209 where the liquid ammonia is separated out. The liquid ammonia enters the liquid ammonia tank 201. The cold gas stream from the ammonia separator enters refrigeration exchanger 201 for refrigeration exchange, which is pressurized in the recycle compressor, converges with incoming make-up gas, enters the recycle gas heat exchanger and is heated before entering the ammonia reactor, where the loop completes.